CVE-2026-52734 ZEBRA: Unbounded memory leak in mempool download pipeline via timeout path cancel_handles retention

ZEBRA is a Zcash node written entirely in Rust. Prior to 4.5.0, an unauthenticated P2P peer can cause the mempool download pipeline to retain transactions after verification reaches the outer RATELIMITDELAY timeout. In zebrad/src/components/mempool/downloads.rs, Downloads::pollnext removed...